CVE-2026-31700— net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()

net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()

In the Linux kernel, the following vulnerability has been resolved: net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() In tpacket_snd(), when PACKET_VNET_HDR is enabled, vnet_hdr points directly into the mmap'd TX ring buffer shared with userspace. The kernel validates the header via __packet_snd_vnet_parse() but then re-reads all fields later in virtio_net_hdr_to_skb(). A concurrent userspace thread can modify the vnet_hdr fields between validation and use, bypassing all safety checks. The non-TPACKET path (packet_snd()) already correctly copies vnet_hdr to a stack-local variable. All other vnet_hdr consumers in the kernel (tun.c, tap.c, virtio_net.c) also use stack copies. The TPACKET TX path is the only caller of virtio_net_hdr_to_skb() that reads directly from user-controlled shared memory. Fix this by copying vnet_hdr from the mmap'd ring buffer to a stack-local variable before validation and use, consistent with the approach used in packet_snd() and all other callers.

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

N/A

Linux kernel 安全漏洞

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于tpacket_snd()中mmap d vnet_hdr存在TOCTOU竞争条件，可能导致并发用户空间线程修改vnet_hdr字段绕过安全检查。

N/A

N/A